The invention relates to an apparatus for injecting or feeding pulverulent or dry pulverized material into a conveying or feed pipe under an overpressure by an overhead-mounted worm, or screw whose worm casing is extended beyond the end of the worm, to a check valve positioned at the start of the conveying or feed pipe.
German Pat. No. 25 07 687 relates to an apparatus of the aforementioned type and describes in detail the problem occurring with such apparatus. The length of the portion of the worm casing, which projects beyond the worm in the direction of the check valve is very critical in narrow limits in order to form a material plug of the correct length, which ensures an adequate seal, but requires the minimum additional energy. In order to be able to adjust the length of this portion within narrow limits in such a way that the material plug has the corresponding desired length, German Pat. No. 25 07 687 proposed placing rings of varying thickness in front of the check valve for extending the worm casing and as a result it is possible to adjust the corresponding portion of said casing.
In another known apparatus, namely a concrete pump, it has already been proposed to provide a conically widening accumulation portion following the worm. In the case of such so-called concrete pumps the seal is not as critical as in the apparatus of the aforementioned type, because the material only has to be conveyed against a relatively low overpressure determined by the conveying air introduced following the accumulation portion.